Spring vices of this type have been known for a long time. For example, EP 0 271 782 B1 discloses a spring vice that comprises a central tensioning device that can be detachably engaged with two disk-shaped pressure plates for tensioning a coil spring. In this prior-art spring vice, the tensioning device comprises a total of three tubular elements, which can be pushed into one another in a telescopic manner. The tubular element with the smallest diameter has positive-locking elements at its free end, with which the tensioning device can be brought into positive-locking engagement with the first pressure plate. To make it possible to engage the pressure plate with these positive-locking elements, a corresponding opening is provided in the pressure plate, through which the tensioning device with its positive-locking elements can be passed and can be brought into positive-locking engagement with depressions in the edge area of the opening. This end tube of the tensioning device, which end tube is designed as a threaded tube, is telescopically in connection via an intermediate tube with a so-called housing tube, which is likewise provided with positive-locking elements in its end area located opposite the positive-locking elements of the threaded tube.
The second pressure plate of this prior-art spring vice is in turn likewise provided with a central opening, with which it can be brought into fixed engagement with this positive-locking element of the housing tube. The two pressure plates have an essentially round basic shape each and are first inserted into the spring turns of the coil spring to be accommodated for tensioning a coil spring. The tensioning device is subsequently passed through the openings of the two pressure plates and is correspondingly brought into engagement with the openings of the pressure plates in a fixed manner. The manner of correctly attaching the prior-art spring vice as well as of the tensioning operation during the tensioning of a coil spring is described in greater detail in EP 0 271 782 B1, so that reference is made in this respect to this document.
In this prior-art embodiment of the spring vice, the openings are arranged concentrically in the approximately round, disk-shaped pressure plates, so that the tensioning device is aligned essentially coaxially to the coil spring to be tensioned within the spring turns of this coil spring during the tensioning of a coil spring. By actuating the drive of the tensioning device, which drive is designed as a spindle drive, the distance between the pressure plates in the axial direction of the coil spring to be tensioned is shortened during the tensioning operation, so that the coil spring is inevitably tensioned. To actuate the tensioning device, a threaded spindle, which is provided with an axially projecting wrench profile in the area of the positive-locking elements of the housing tube, is provided in the tubular elements. The threaded spindle engages with its other end the threaded tube of the tensioning device located opposite the wrench profile, so that the tensioning device is shortened during the actuation of the threaded spindle. It is obvious that the threaded spindle is supported now on the drive side axially via a thrust bearing in a head part of the housing tube in the area of its wrench profile.
Thus, the housing tube with its positive-locking element forms a kind of adjusting member, which is moved toward the positive-locking elements of the threaded tube by actuating the threaded spindle, as a result of which the tensioning of a coil spring is brought about. For receiving a spring turn or at least a partial area of the spring turn of the coil spring to be tensioned, the pressure plates have in turn circular tensioning surfaces which correspond to the coil spring to be tensioned and are radially limited toward the inside and the outside. These tensioning surfaces are provided with a slope in the circumferential direction, so that the radially inner and outer limitation is formed by a corresponding limiting edge provided in these edge areas. These tensioning surfaces are also arranged essentially concentrically in the pressure plates, so that the spring turns are received concentrically in each pressure plate. An essentially concentric alignment of the tensioning device within the coil spring to be tensioned during the tensioning operation is also achieved due to this design of the tensioning surfaces. To pass the spring turns not being grasped by the pressure plates through the particular pressure plate, the tensioning surfaces are interrupted in the circumferential direction by a recess, through which the coil springs can be passed in the axial direction and in the circumferential direction.
In this prior-art spring vice, the tensioning device becomes shorter during the tensioning of the coil spring due to the special design, so that considerable advantages are obtained especially during the removal and mounting of a coil spring on a motor vehicle. For example, coil springs tensioned completely to a stop can be removed from the spring plates of a motor vehicle axle together with the spring vice due to this telescopic shortening of the tensioning device without the axle of the motor vehicle having to be removed.
Such spring vices having a similar design acting in the same manner have also been known, e.g., from EP 0 115 774, and the design of these spring vices is essentially identical in terms of the mode of operation to that of the above-described spring vice according to EP 0 271 782 B1. Reference is made in this respect to these two documents, which show the detailed design as well as the mode of operation of these prior-art spring vices.
Other spring vices of this class have been known as well, whose tensioning device cannot be shortened telescopically, but whose mode of operation is at least similar to that of the above-described spring vices. A relatively long threaded spindle is provided in these spring vices, and positive-locking elements, with which the first pressure plate can be brought into engagement in a replaceable and positive-locking manner, is provided at one end of the said threaded spindle. The second pressure plate is brought into engagement in a positive-locking manner with an approximately cylindrical adjusting member. This adjusting member is mounted axially adjustably on the threaded spindle and is displaced by means of an adjusting nut along the threaded spindle toward the first pressure plate during the tensioning of a coil spring, i.e., the threaded spindle and the adjusting nut form the spindle drive in this type of spring vice, the adjusting nut being provided with the wrench profile. Since the tensioning device is not shortened in a telescopic manner during the tensioning operation in this type of spring vice, the vehicle axle must be removed for inserting and removing the coil spring. These spring vices, which likewise cannot be shortened in a telescopic manner, also share a common feature with the above-described spring vices, namely, that a concentric alignment of the tensioning device in relation to the coil spring to be tensioned is achieved due to the central arrangement of the openings in the likewise round pressure plates.
To make it possible to introduce the tensioning device into the spring and to engage it with the pressure plates, the spring plate, from whose side the tensioning device is to be introduced into the coil spring, has a passage opening through which the tensioning device can be passed. Depending on the design of the axle, the upper spring plate seated on the vehicle body or also the lower spring plate seated on the movable axle body has such a passage opening. A corresponding passage opening, which is either directly adjacent to the passage opening of the spring plate or is located at a certain distance therefrom, which applies especially to the passage opening of the axle body, is likewise present now in the body or in the axle body. It shall be noted that axle bodies in which a type of spring plate is integrated as a one-piece component in the axle body as a spring mount have been known as well.
It was now found that the accessibility of the drive of the spring vice is often limited especially during the tensioning of coil springs that are pretensioned in a slightly bent form in the installed state and/or of coil springs installed between two spring plates arranged offset at right angles to the longitudinal axis of the spring. In such predetermined axle designs, the coil spring has a sloped shape in the installed state, whereas the passage opening of the axle body and the passage opening of the corresponding spring plate or the spring mount integrated in the axle body are arranged concentrically to one another. This in turn causes that when the spring vice is attached correctly to the coil spring, the spring vice with its tensioning device follows the sloped shape of the coil spring, i.e., the tensioning device assumes an oblique position in relation to the axle body when the pressure plates are correctly inserted into the coil spring and the tensioning device has been brought into engagement with the pressure plates, as a result of which the access to the drive, which is located within the axle body in the correctly attached state of the tensioning device, is made at least considerably difficult or becomes altogether impossible. Furthermore, the pressure plate tends to jam or tilt on the tensioning device, especially during the tensioning of the coil springs pretensioned in a bent form, when the pressure plate is to be brought into engagement with the coil springs, i.e., when the tensioning device must be pushed through the pressure plates in order to be brought into engagement with them.